A gradient of auxin and auxin-dependent transcription precedes tropic growth responses
A gradient of auxin and auxin-dependent transcription precedes tropic growth responses
复制标题
DOI：
10.1073/pnas.0507127103
复制
发表时间：
2006-01-03
影响因子：
11.1
通讯作者：
Liscum, E
中科院分区：
文献类型：
--
作者：
Esmon, CA;Tinsley, AG;Liscum, E
植物，虽然无柄，可以重新调整生长轴，以应对不断变化的环境条件。向光性和向重力性分别代表光方向和生长轴方向相对于重力方向的变化诱导的适应性生长反应。近80年的Cholodny-Went理论[Went，F。W. & Thimann，K. V.（1937）Phytohormons（Macmillan，纽约）]预测，植物形态发生素生长素梯度的形成对于热带曲率的建立至关重要。缺乏生长素调节的转录激活因子NPH 4/ARF 7的拟南芥突变体的幼苗茎中的向性反应的丧失进一步表明，基因表达的梯度代表了生长素梯度的基本输出。然而，这些输出成分的分子身份，这可能是编码蛋白质直接参与生长控制，仍然难以捉摸。在这里，我们报告发现了一套热带刺激诱导的基因在甘蓝，生长素梯度和表现出形态学分级表达伴随着，或之前，可观察到的曲率反应。这些结果为Cholodny-Went理论提供了令人信服的分子支持，并表明形态学分级转录是解释生长素热带刺激梯度的重要机制。有趣的是，两个热带刺激诱导的基因，EXPA 1和EXPA 8，编码参与细胞壁延伸的酶，这是导致弯曲的差异生长的先决条件，并且在侧翼弯曲之前上调，这将延长。这一观察结果表明，形态学分级转录可能导致蛋白质的分级表达，其活性可以直接调节热带曲率的建立和调节。
Plants, although sessile, can reorient growth axes in response to changing environmental conditions. Phototropism and gravitropism represent adaptive growth responses induced by changes in light direction and growth axis orientation relative to gravitational direction, respectively. The nearly 80-year-old Cholodny-Went theory [Went, F. W. & Thimann, K. V. (1937) Phytohormones (Macmillan, New York)] predicts that formation of a gradient of the plant morphogen auxin is central to the establishment of tropic curvature. Loss of tropic responses in seedling stems of Arabidopsis thaliana mutants lacking the auxin-regulated transcriptional activator NPH4/ARF7 has further suggested that a gradient of gene expression represents an essential output from the auxin gradient. Yet the molecular identities of such output components, which are likely to encode proteins directly involved in growth control, have remained elusive. Here we report the discovery of a suite of tropic stimulus-induced genes in Brassica oleracea that are responsive to an auxin gradient and exhibit morphologically graded expression concomitant with, or before, observable curvature responses. These results provide compelling molecular support for the Cholodny-Went theory and suggest that morphologically graded transcription represents an important mechanism for interpreting tropically stimulated gradients of auxin. Intriguingly, two of the tropic stimulus-induced genes, EXPA1 and EXPA8, encode enzymes involved in cell wall extension, a response prerequisite for differential growth leading to curvatures, and are up-regulated before curvature in the flank that will elongate. This observation suggests that morphologically graded transcription likely leads to the graded expression of proteins whose activities can directly regulate the establishment and modulation of tropic curvatures.